The present invention pertains to a process for preparing integral skin polyurethane foam. In particular the invention relates to a process for preparing an integral skin foam wherein water is the main blowing and density controlling agent. The use of water as the blowing agent obviates the need to use chlorofluorocarbons which have been shown to be of detriment to the environment. Although the products of this process may exhibit a wide range of densities and hardness'; it is those products referred to as low density, flexible, integral skin foams that are of particular interest.